FERMI-LAT OBSERVATIONS OF THE DIFFUSE gamma-RAY EMISSION: IMPLICATIONS FORCOSMIC RAYS AND THE INTERSTELLAR MEDIUM

Ackermann M, Ajello M, Atwood WB, Baldini L, Ballet J, Barbiellini G, Bastieri D, Bechtol K, Bellazzini R, Berenji B, Blandford RD, Bloom ED, Bonamente E, Borgland AW, Brandt TJ, Bregeon J, Brigida M, Bruel P, Buehler R, Buson S, Caliandro GA, Cameron RA, Caraveo PA, Cavazzuti E, Cecchi C, Charles E, Chekhtman A, Chiang J, Ciprini S, Claus R, Cohen-Tanugi J, Conrad J, Cutini S, De Angelis A, De Palma F, Dermer CD, Digel SW, Do Couto E Silva E, Drell PS, Drlica-Wagner A, Falletti L, Favuzzi C, Fegan SJ, Ferrara EC, Focke WB, Fortin P, Fukazawa Y, Funk S, Fusco P, Gaggero D, Gargano F, Germani S, Giglietto N, Giordano F, Giroletti M, Glanzman T, Godfrey G, Grove JE, Guiriec S, Gustafsson M, Hadasch D, Hanabata Y, Harding AK, Hayashida M, Hays E, Horan D, Hou X, Hughes RE, Johannesson G, Johnson AS, Johnson RP, Kamae T, Katagiri H, Kataoka J, Knoedlseder J, Kuss MW, Lande J, Latronico L, Lee SH, Lemoine-Goumard M, Longo F, Loparco F, Lott B, Lovellette MN, Lubrano P, Mazziotta MN, Mcenery JE, Michelson PF, Mitthumsiri W, Mizuno T, Monte C, Monzani ME, Morselli A, Moskalenko IV, Murgia S, Naumann-Godo M, Norris JP, Nuss E, Ohsugi T, Okumura A, Omodei N, Orlando E, Ormes JF, Paneque D, Panetta JH, Parent D, Pesce-Rollins M, Pierbattista M, Piron F, Pivato G, Porter TA, Raino S, Rando R, Razzano M, Razzaque S, Reimer A, Reimer O, Sadrozinski HFW, Sgro C, Siskind EJ, Spandre G, Spinelli P, Strong AW, Suson DJ, Takahashi HH, Tanaka T, Thayer JG, Thayer JB, Thompson DJ, Tibaldo L, Tinivella M, Torres DF, Tosti G, Troja E, Usher TL, Vandenbroucke J, Vasileiou V, Vianello G, Vitale V, Waite AP, Wang P, Winer BL, Wood KS, Wood M, Yang Z, Ziegler M, Zimmer S (2012)

Publication Type: Journal article

Publication year: 2012

Journal

Book Volume: 750

Journal Issue: 1

DOI: 10.1088/0004-637X/750/1/3

Abstract

The gamma-ray sky >100MeVis dominated by the diffuse emissions from interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way. Observations of these diffuse emissions provide a tool to study cosmic-ray origin and propagation, and the interstellar medium. We present measurements from the first 21 months of the Fermi Large Area Telescope (Fermi-LAT) mission and compare with models of the diffuse gamma-ray emission generated using the GALPROP code. The models are fitted to cosmic-ray data and incorporate astrophysical input for the distribution of cosmic-ray sources, interstellar gas, and radiation fields. To assess uncertainties associated with the astrophysical input, a grid of models is created by varying within observational limits the distribution of cosmic-ray sources, the size of the cosmic-ray confinement volume (halo), and the distribution of interstellar gas. An all-sky maximum-likelihood fit is used to determine the X-CO factor, the ratio between integrated CO-line intensity and H-2 column density, the fluxes and spectra of the gamma-ray point sources from the first Fermi-LAT catalog, and the intensity and spectrum of the isotropic background including residual cosmic rays that were misclassified as gamma-rays, all of which have some dependency on the assumed diffuse emission model. The models are compared on the basis of their maximum-likelihood ratios as well as spectra, longitude, and latitude profiles. We also provide residual maps for the data following subtraction of the diffuse emission models. The models are consistent with the data at high and intermediate latitudes but underpredict the data in the inner Galaxy for energies above a few GeV. Possible explanations for this discrepancy are discussed, including the contribution by undetected point-source populations and spectral variations of cosmic rays throughout the Galaxy. In the outer Galaxy, we find that the data prefer models with a flatter distribution of cosmic-ray sources, a larger cosmic-ray halo, or greater gas density than is usually assumed. Our results in the outer Galaxy are consistent with other Fermi-LAT studies of this region that used different analysis methods than employed in this paper.

Authors with CRIS profile

Involved external institutions

Deutsches Elektronen-Synchrotron DESY Germany (DE) Stanford University United States (USA) (US) University of California Santa Cruz United States (USA) (US) National Institute for Nuclear Physics / Istituto Nazionale di Fisica Nucleare (INFN) Italy (IT) University of Paris 7 - Denis Diderot / Université Paris VII Denis Diderot France (FR) Institut de Recherche en Astrophysique et Planétologie (IRAP) France (FR) Politecnico di Bari Italy (IT) École Polytechnique - Université Paris-Saclay France (FR) Institut de Ciències de l'Espai (ICE) Spain (ES) National Institute for Astrophysics / Istituto Nazionale Astrofisica (INAF) Italy (IT) Italian Space Agency / Agenzia Spaziale Italiana (ASI) Italy (IT) Università degli Studi di Perugia Italy (IT) University of Montpellier / Université Montpellier France (FR) University of Udine / Università degli Studi di Udine Italy (IT) U.S. Naval Research Laboratory United States (USA) (US) National Aeronautics and Space Administration (NASA) United States (USA) (US) University of Alabama in Huntsville (UAH) United States (USA) (US) Hiroshima University Japan (JP) Université Bordeaux 1, Sciences et Technologies France (FR) Ohio State University United States (USA) (US) University of Iceland (UI) / Háskóli Íslands Iceland (IS) Ibaraki University / 茨城大学 Japan (JP) Stockholm University / Stockholms universitet Sweden (SE) Waseda University / 早稲田大学 Japan (JP) Kyoto University / 京都大学 Kyōto daigaku Japan (JP) Boise State University United States (USA) (US) University of Denver United States (USA) (US) George Mason University United States (USA) (US) University of Padua / Universita degli Studi di Padova Italy (IT) NYCB Real-Time Computing, Inc. United States (USA) (US) Max-Planck-Institut für extraterrestrische Physik (MPE) / Max Planck Institute for Extraterrestrial Physics Germany (DE) Purdue University Northwest / Purdue University Calumet United States (USA) (US)

How to cite

APA:

Ackermann, M., Ajello, M., Atwood, W.B., Baldini, L., Ballet, J., Barbiellini, G.,... Zimmer, S. (2012). FERMI-LAT OBSERVATIONS OF THE DIFFUSE gamma-RAY EMISSION: IMPLICATIONS FORCOSMIC RAYS AND THE INTERSTELLAR MEDIUM. Astrophysical Journal, 750(1). https://doi.org/10.1088/0004-637X/750/1/3

MLA:

Ackermann, Markus, et al. "FERMI-LAT OBSERVATIONS OF THE DIFFUSE gamma-RAY EMISSION: IMPLICATIONS FORCOSMIC RAYS AND THE INTERSTELLAR MEDIUM." Astrophysical Journal 750.1 (2012).

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